@@ -4432,6 +4432,7 @@ static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf)
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_super_block *es = sbi->s_es;
u64 fsid;
+ s64 bfree;
if (test_opt(sb, MINIX_DF)) {
sbi->s_overhead_last = 0;
@@ -4475,8 +4476,10 @@ static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf)
buf->f_type = EXT4_SUPER_MAGIC;
buf->f_bsize = sb->s_blocksize;
buf->f_blocks = ext4_blocks_count(es) - sbi->s_overhead_last;
- buf->f_bfree = percpu_counter_sum_positive(&sbi->s_freeblocks_counter) -
+ bfree = percpu_counter_sum_positive(&sbi->s_freeblocks_counter) -
percpu_counter_sum_positive(&sbi->s_dirtyblocks_counter);
+ /* prevent underflow in case that few free space is available */
+ buf->f_bfree = max_t(s64, bfree, 0);
buf->f_bavail = buf->f_bfree - ext4_r_blocks_count(es);
if (buf->f_bfree < ext4_r_blocks_count(es))
buf->f_bavail = 0;
I found the issue that the number of free blocks went negative. # stat -f /mnt/mp1/ File: "/mnt/mp1/" ID: e175ccb83a872efe Namelen: 255 Type: ext2/ext3 Block size: 4096 Fundamental block size: 4096 Blocks: Total: 258022 Free: -15 Available: -13122 Inodes: Total: 65536 Free: 63029 f_bfree in struct statfs will go negative when the filesystem has few free blocks. Because the number of dirty blocks is bigger than the number of free blocks in the following two cases. CASE 1: ext4_da_writepages mpage_da_map_and_submit ext4_map_blocks ext4_ext_map_blocks ext4_mb_new_blocks ext4_mb_diskspace_used percpu_counter_sub(&sbi->s_freeblocks_counter, ac->ac_b_ex.fe_len); <--- interrupt statfs systemcall ---> ext4_da_update_reserve_space percpu_counter_sub(&sbi->s_dirtyblocks_counter, used + ei->i_allocated_meta_blocks); CASE 2: ext4_write_begin __block_write_begin ext4_map_blocks ext4_ext_map_blocks ext4_mb_new_blocks ext4_mb_diskspace_used percpu_counter_sub(&sbi->s_freeblocks_counter, ac->ac_b_ex.fe_len); <--- interrupt statfs systemcall ---> percpu_counter_sub(&sbi->s_dirtyblocks_counter, reserv_blks); To avoid the issue, this patch ensures that f_bfree is non-negative. Signed-off-by: Kazuya Mio <k-mio@sx.jp.nec.com> --- fs/ext4/super.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html